Single-ended halogen incandescent lamps have, usually, a cylindrical bulb of transparent material, a base, and an axially extending coiled incandescent filament. The filament extends from a base end to a remote end, and is held in position by a filament mount which is coupled, electrically and mechanically, to the respective ends of the filament. The filament mount is retained in position in the lamp by a cross bar of non-conductive material, typically quartz, or a similar material. Two internal current supply leads pass through the cross bar and are retained in position thereby, the internal current supply leads and the cross bar together forming a filament mount assembly. One of the current supply leads extends along the inner wall of the bulb towards the remote end of the filament to provide an electrical connection therefor and possibly also to hold it in position. The other of the current supply leads is connected to the base end of the filament. The current supply leads which extend outwardly from the cross bar are connected to a standard connection arrangement which, for example, is formed by molybdenum foils, connected to external current supply leads, the molybdenum foils being held in the bulb by a pinch or press seal.
Halogen incandescent lamps of this type are suitable for operating voltages in the range of about 50 V to 250 V, and can be constructed with nominal power ratings of, for example, between about 40 W to 150 W.
It has been proposed to determine the position of the current supply lead which extends to the remote end of the filament, which will also be referred to as the first current supply lead, by securing it in, or on an exhaust tip formed at the remote end of the bulb (see, for example, German Utility Model DE-GM 68 04 136). Such a construction is expensive and difficult to make, and extends the overall length of the lamp. It is difficult to produce such lamps, particularly under mass production conditions. Difficulties arise upon fitting of the filament in the mount and when flushing the lamp and cleaning it; exact centering of the filament in the lamp axis is difficult to obtain, yet such centering is desirable for applications where reflection of radiation from the filament is of importance.
Some lamps have been proposed in which the first current supply lead connected to the remote end of the filament is bent, with its free end, in circular form, which is tightly engaged against the inner wall of the glass bulb, see for example U.S. Pat. No. 3,898,505, Danko (assigned General Electric). This arrangement improves the centricity of the filament, but requires precise manufacture of the loop to engage the wall. This loop must be somewhat springy to account for tolerances in the bulb. The springiness of the loop, which is considerable, will be transferred in the form of vibrations and oscillations to the filament if the lamp is retained in an unstable socket or fitting (see U.S. Pat. No. 3,982,145, Liptow, discussed below).
Circular loops to maintain a filament in position have also been proposed for lamps of the "Lumiline" type, which are double-ended lamps having an elongated filament. The filament is supported along the length of the lamp by several circular loops (see for example U.S. Pat. No. 3,982,145, Liptow, assigned General Electric). As an alternative to circular loops, the elongated filament can also be held in position in central loops which are placed within polygons, preferably seven-cornered polygons. It is very difficult to make such holders.
The German Utility Model Publication DE-GM 73 10 947 describes a holder for such elongated lamp filaments which engages the wall of the lamp at three points. The arrangement, in effect, is similar to a triangle within a circle. The filament is held from one of the sides of the triangle, which, rather than being one straight line, is formed of two radially directed leg portions. Alternatively, a part-circular loop, extending spirally towards the center, can be used in order to hold the filament. This holder, like the previous elongated lamp types, requires that the filament is threaded through a central holding portion of the holder structures. This is difficult to carry out in practice. The arrangement, further, will transfer vibration and shock forces affecting the filament to the holder structures. Upon being subjected to shock, the filament may shift substantially from the central or quiescent position, which changes the angular relationships of the triangle.
Holders for "Lumiline" or elongated type double-ended lamps are used to prevent sag of the very long filament structure, particularly if the lamp is operated in horizontal position. Such sag interferes with proper operation of the halogen incandescent lamp.
Single-ended halogen incandescent lamps have filaments which are substantially shorter than those of the double-ended lamp type. It is usually not necessary to provide extensive support systems for the filament to prevent sagging thereof in operation. On the other hand, however, the holder which at the same time also forms the current supply must unambiguously and reliably determine the position of the filament, for example the axial position thereof coaxial with the axis of the lamp. At the base end, this is simple since the associated current supply lead is fixed in position in the press seal and extends only a short distance therebeyond. To support the remote end of the filament in position, however, is much more difficult since it is supported and supplied by current from the free end of the first or internally extending current supply lead, which extends in parallel to the filament within the bulb itself.